A leading Australian Catholic legal thinker has reversed his opposition to the idea of same-sex couples being able to wed legally.

Father Brennan, a Jesuit priest and professor of law at the Australian Catholic University, previously opposed marriage equality despite being a high profile advocate for human rights and social justice – although he had previously expressed that civil unions might be ok.

In an article published today in the progressive Catholic journal Eureka Street Brennan wrote, ‘I believe the secular Australian state should be able to recognize same-sex marriage.’

‘I also believe that this change should legally exempt religious institutions from any requirement to change their historic position and practice that marriage is exclusively between a man and a woman.

‘It is high time to draw a distinction between a marriage recognized by civil law and a sacramental marriage.

‘I now accept that we can probably no longer draw a line between civil unions and same sex marriage. That will be the long term consequence of last month's US Supreme Court decisions which will impact much further west than California.

‘Society could properly move to recognition of civil unions or same sex marriage if and when the overwhelming majority of the population (including those who are presently married civilly) supported such change.’

‘In deciding whether to expand civil marriage to the union of two persons of the same gender, legislators should have regard not just for the wellbeing of same sex couples and the children already part of their family units, but also for the wellbeing of all future children who may be affected, as well as the common good of society in setting appropriate contours for legally recognized relationships,’ Brennan wrote.

‘Same sex couples wanting to create their own children may in the foreseeable future be able to use only their own genetic material, precluding the possibility that such children will have a biological father and a biological mother. Whether or not we legislate for same sex marriage, we should restrict artificial reproduction of children such that they will have a biological father and a biological mother, and hopefully able to be known by them.

‘Legislators making laws regarding adoption ought be able to demand that adoption agencies continue to consider the best interests of the child. In the case of a child unrelated to any prospective adopting couple, the adoption agency ought be able to have regard to the desirability of a child being brought up in a family with an adult male and an adult female.’

Australian Marriage Equality national convener Rodney Croome welcomed Brennan’s support for reform on the issue.

‘Fr Brennan is a widely respected defender of human rights and dignity, so his change of heart on marriage equality will carry great weight among Catholics and non-Catholics alike,’ Croome said.

‘While I disagree with Fr Brennan that two-mum and two-dad families are second-best, his distinction between who makes the best parents and who should be permitted to legally marry is an important one that other Christians should seriously consider,’ Croome said.

‘Given that every Australian opinion poll for seven years has shown majority support for marriage equality I believe Fr Brennan's threshold for the nation enacting marriage equality has already been met.’